I'm another who enjoys time on the ship and for our upcoming Caribbean trip am not planning and Port Adventures at either port except possibly walking off the ship and looking at the port shops.
That being said, the opportunity for a day at WDW with Park Hoppers would have me leaving the ship early and making the most of an amazing day at WDW! We'd hit MK and possibly one other park. We've done a day once where we hit all 4 parks in one day and while it was fun to say we've done it once, we spent a lot of time moving between parks, going through security, getting into the parks and to the attractions. Not something I'd personally choose to do often and for us, not when we only have 1 day at the parks.
You'll have a great time whatever you choose to do! You're either at WDW or on a Disney ship! A win-win for sure!!!